Internal combustion engines having fuel injectors associated with each cylinder are known. A typical fuel injector is positioned beneath the valve cover of the engine and in direct fluid communication with the cylinder. The fuel injector includes various valves and valve arrangements that inject fuel into the cylinder in a controlled fashion. These valves are controlled, typically, by electronic actuators associated with each fuel injector. Each fuel injector is capable of injecting a quantity of fuel into a cylinder of an internal combustion engine at pre-determined times and for pre-determined durations. During operation, electrical signals sent to the electronic actuator are used to control the valve that injects fuel into the cylinder.
Modern engines inject fuel into their cylinders at high pressures. Compression of fuel at a high pressure increases fuel temperature, which in turn increases the temperature within the fuel injector during operation of the engine. The current trend is to increase injection pressures for fuel injected into internal combustion engines. This creates potential thermal issues, which are related to maintaining the temperature of internal components of the fuel injector within pre-determined ranges. Moreover, increased temperatures of the fuel injector, and the injected fuel, tend to increase the oxidization of fuel being injected. This oxidation has the potential to deposit debris on various surfaces of the injector valves.
One known arrangement for providing cooling to a fuel injector can be found in U.S. Pat. No. 4,958,101, granted on Sep. 18, 1990 and assigned on its face to Toyota Jidosha Kabushiki Kaisha, of Japan (the '101 patent). The '101 patent discloses a fuel injector having a piezoactuator associated with a piston. The piston is disposed within a piston bore of a housing and is surrounded by a hollow cylindrical resilient member that applies a compressive load on the actuator. An annular cooling chamber is formed between the piston and the actuator housing. The hollow cylindrical resilient member is inserted into the cooling chamber to bias the piston upward. When a charge is applied to the piezoelectric element, the piezoelectric element expands axially, and as a result, the piston is extended to compress a quantity of fuel to be injected. When the charge of the piezoelectric element is discharged, the piezoelectric element axially contracts, pulling in additional fuel at a supply pressure to be compressed.
Fuel in the annular cooling volume is provided at the same supply pressure as fuel that is injected. When an injection has been completed, additional fuel is pulled into various internal cavities of the fuel injector. The fuel being drawn into various functional volumes of the fuel injector includes fuel coming from the annular cooling volume, which enters a supply passage via a check valve. One disadvantage of mixing cooling fuel with injection fuel is the resulting elevation in the temperature of the injected fuel. For example, heat removed from the piezoactuator of the device disclosed in the '101 patent may increase the temperature of the injected fuel. Moreover, such increase of temperature may further increase the rate of deposit formation on various internal components of the fuel injector.